Asterisk & portasip

i am using asterisk with a service provider who is using portasip as his proxy server. i am able to make outgoing calls only after i have changed the user agent to read “portasipfriendly” and NOT “asterisk” because with asterisk it will not work.

my question is: i am not able to receive calls, anyone has gone through this problem and was able to find a solution.

thanks